Actually, I searched some more and found slightly conflicting info. Some of the sites such as Monstercat's twitter would word the announcement as following (https://twitter.com/Monstercat/status/872150197043953665):
And Here We Go! @tokyomachine “ROCK IT” launches the preorder for @RocketLeague X Monstercat Vol 1. today!
The link points to streaming services for the Tokyo Machine's single "Rock It" and to stores for the "Rocket League x Monstercat, Vol. 1" album.
But some sites would word it as following (http://www.youredm.com/2017/06/06/monstercat-x-rocket-league/):
The album is available for pre-order now and comes with an exclusive download of “ROCK IT” by Tokyo Machine (the song from Rocket League’s 2nd anniversary update trailer)
However, the song is already present on the album, so why would they add it as an exclusive download as well? I think they just worded it poorly, because according to google search, only 4 unique sites display it this way (literally the same copy-pasted wording template). I might be wrong, though.